Inversion of the Verb after certain adverbials
Certain adverbials, mostly with a restrictive or negative sense, can be placed at the beginning of the sentence for emphasis, and are then followed by the inverted (interrogative) form of the verb: Never, seldom, scarcely, ever, no sooner... than..., nowhere, in no circumstances, only then, only when, only in this way, not only, so, neither, nor
I have never before been asked such a question
Never before have I been asked such a question
No sooner had they left the house when the storm broke
Not only were we robbed, they also beat us up!
So neurotic did he become that no one could stand living with him any longer
The adverbs: in, out, up, down, round, over, back, forward, etc. when placed at the beginning of a sentence are followed by V + S when the S is not a pronoun:
In came Joanne
In she came
Up jumped the frog
Up it jumped
Down fell all the contents of my bag!
Down they fell!
Back went my friend again
Back they went again
This is very much used in (children's) story-telling and when we are narrating anecdotes and such. It's very expressive.
Notice I always say in class: Off you go!